1. Field of the Invention
The present invention relates to thin film heads for magnetically writing information on data storage media, and particularly to fabrication processes for manufacturing such heads. Still more particularly, the invention concerns the planarization of device layer surfaces in thin film magnetic write heads using chemical mechanical polishing techniques.
2. Description of the Prior Art
By way of background, thin film magnetic write heads conventionally include a P2 pole piece having a sloping surface that extends toward the pole tip area where the head's write gap is located. An example of this conventional geometry is shown in the FIG. 1, which illustrates a side view of a prior art write head 2 in which the ABS (Air Bearing Surface) of the head is on the right side of the figure. The P2 pole piece 4 lies over an integrated layer 6 containing plural copper coils 8 surrounded by insulative hard bake resist material 10. Conventional plating techniques are used to form the P2 pole piece 4 over the integrated layer 6. In particular, after a suitable photoresist mask pattern is applied to define the required P2 yoke configuration, a ferromagnetic material such as an Ni—Fe alloy (permalloy) is plated from a liquid or gaseous medium or deposited using any known deposition method. A disadvantage of this technique is that the ill-defined slope 12 of the integrated layer 6 as it approaches the pole tip 14 makes it difficult to control the geometry of the P2 photoresist mask. In addition, the application of P2 material onto the integrated layer's sloped surface can produce a P2 layer having non-uniform thickness and varying ferromagnetic properties. A further disadvantage is that write head track width is difficult to control. Each of the foregoing problems may be present to different degrees in any given write head of a single fabrication batch, or between write heads produced in different fabrication batches. This makes repeatability of results difficult to achieve and reduces production yields accordingly.
As a solution to the foregoing design problem, applicants' assignee previously developed a write head design in which the sloping P2 pole layer of the prior art write head is replaced with a combined P2/P3 structure that has no sloping surfaces. One example of this design approach is shown in FIG. 2, which illustrates an improved write head 20 in which the ABS is on the left side of the figure. The write head 20 includes a P1 pole layer 22 covered by an integrated layer 24 containing plural copper coils 26 surrounded by insulative hard bake resist material 28. After a first alumina dielectric layer 30 is added, a combined P2/P3 pole piece 32 is formed. Initially, only a pair of small P2 stubs 34a and 34b are placed at the write head back gap and at the P2 pole tip, respectively. After applying and patterning a second alumina dielectric layer 36, a horizontal P3 pole piece 38 is added to magnetically interconnect the P2 stubs 34a and 34b. Note that the device layers below the P1 pole layer 22 are conventional in nature and are collectively referred to in the drawing figures as “other structure” for convenience.
It has been determined that the most preferred approach to fabricating the write head 20 would be to utilize a CMP (Chemical Mechanical Polishing) planarization step prior to deposition of the second alumina dielectric layer 36 and the P3 pole piece 38. In particular, after formation of the copper coils 26, the hardbaked resist material 28, the first alumina dielectric layer 30, and the NiFe P2 stubs 34a/34b, these structures should be planarized to provide a flat horizontal surface onto which the second alumina dielectric layer 36 and the P3 pole piece 38 can be applied.
CMP is a known technique for planarizing various structures on a thin film substrate. The process creates a smooth planar surface for optimal lithographic processing steps of the intermediate thin film fabrication process. CMP planarization processing is used not only to planarize protruding surfaces, but also to remove undesirable residues that remain from other substrate processing steps.
The difficulty with using CMP planarization for the improved write head application described above is that current CMP methods will not polish away the four involved materials (copper, hardbaked resist, alumina and NiFe) at the same rate. These materials are removed at different rates, resulting in an uneven surface profile, particularly between the hardbaked resist and copper structures, and between the hardbaked resist and alumina structures.
Accordingly, an improved CMP planarization method is required if improvements in the fabrication of the above-described write head design are to be achieved. What is needed is a new CMP planarization process wherein a structure comprising copper, hardbaked resist, alumina and NiFe can be simultaneously polished in a way that facilitates more equal removal of the materials being planarized.